Browsing by Author "Asrat, Asfawossen (PhD)"
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Item Analysis of Subsurface Contaminant Transport in Akaki Well Field and surrounding areas, Central Ethiopia(Addis Ababa Universty, 2007-08) Gudissa, Leta; Asrat, Asfawossen (PhD)The acute need for water in big cities like Addis Ababa calls for an integrated water resources development approach that considers the entailing environmental factors. This task becomes even more pressing as industrialization and development advances. In view of this, the current study aims to identify potential movement of pollutants in a wellfield, and specifically to identify the pathways of pollutants and their spatial movement in the aquifer. The study area, the Akaki well field and surrounding areas including the towns of Kality and Akaki, is located in the Awash drainage basin, southeast of the Addis Ababa city centre. The well field provides more than 30 % of the drinking water supply of Addis Ababa. A groundwater flow model was constructed to analyze contaminant transport in a fractured system. The model was then calibrated with both under steady state and transient state flow conditions, in order to prove that the model represents the actual conditions. Modeling tools have been eventually used to calculate path lines and travel times of contamination. This approach involved the introduction of particles at contaminant sources upstream of wells and at the well field it self, then identifying the path lines, and determining the spatial distribution of the contaminants through steady state flow field at initial step and finally through transient state flow field. The individual measured data for nearly 120 wells were interpolated using kriging method and each cell in the model was assigned its value. The well data base is obtained from AAWSA. The physical parameters are well organized; however, the Hydrochemical data are too old and does not indicate real sign of pollution. The results revealed that the flow lines intersect with the Akaki River in numerous places. Furthermore, the flow lines converge towards Akaki well field from all directions, implying that any contaminated water from the upper part of the aquifer will be pulled into the wells, indicating a high risk of vulnerability of the well field to pollution. The following recommendations are helpful in curbing the risks posed. Manufacturing activities having pollution potential must be limited in special areas sufficiently far from water supply wells; the chemical quality of groundwater must be monitored and Environmental policy must be implemented with particular emphasis for the protection zones around the well field. This study generated a model and recommendations that allows decision makers to establish a framework for regulating contaminants that are likely to pose risks to drinking water in the well-field.Item Analysis on Terrain and Related Challenges in Defense Command Post Site Selection Using Web-Based Gis: a Case of Ada’a District, Eastern Showa Ethiopia(Addis Ababa University, 2015-06-06) Akele, Menbere; Sendabo, Degelo (MR.); Asrat, Asfawossen (PhD)The defense force keeps the sovereignty of the nation and responsibility to the operation of mission success at right time and place to control key terrain areas, to deliver logistics and to combat troops with accurate terrain information. But manually combining terrain information is tiresome, time taking, costy and results vary from expert to expert, therefore the analysis of terrain features for command post best site selection is one of the basic tasks from different military operations and the study provides decision makers and commanders to analyze the terrain visually using automated systems to obtain correct information about the terrain and evaluate the terrain in terms of military aspects. To understand the ground and achieve military goals, the basic sources of information for studying the terrain are topographic maps, aerial photographs, military sketches and sand model. This research paper identifies terrain features for defense command post site selection using RS and GIS techniques and customize and publish maps in web-GIS C4I system for decision makers or commanders. The command post suitable site selection is based on input data layers of elevation, slope, roads, land use land cover, soil types, geological and geomorphological features. The multi-attribute and multi-criteria evaluation methods (GIS with AHP) are used for factor analysis and aggregation. Multi factor analysis or weighted overlay analysis assigns more importance of some criteria over the others. The AHP principle can be used to aggregate the priority for all level of hierarchy structure and the method can be done using any GIS system having overlay capabilities, combine input layers and generate the output command post suitable map. The result showed that optimal sites clearly identified as a higher elevation weight equal to 39% influence is the most important criteria from others. The resulting maps of GIS – AHP indicates best result and suitable location for military command post in Ada’a district.Item Assesment of Soil and Water Contamination Due to Large Scale Floriculture Farming Around Lake Ziway(Addis Ababa University, 2015-05-31) Tsegaye, Tsion; Asrat, Asfawossen (PhD)The main environmental risk of the floricultural production is associated with the extensive use of pesticides and herbicides and the fate of their residues in the soil and water. An intensive use of agrochemicals is taking place in a context of weak and un-harmonized regulations. Nevertheless, the potential of the residues from the horticulture and floriculture systems on surface water resources, particularly Lake Ziway, the freshest water lake; on the top of that, floriculture industries located at the shore discharging untreated effluent directly in to the lake; Both the small scale and large scale floriculture and horticulture farms lack adequately trained personnel for appropriate pesticides management and appropriate organization setup. Moreover, local communities and producers seem to remain largely unaware of the advantages of sustainable management of natural resources leads to environmental degradation such as land, water and soil quality degradations. Therefore, this study was proposed with the objective of assessing the impact of floriculture industries on the soil water quality of the area. The necessary data are collected by direct physical site observation and assessing existing situation of the study area and by taking sample from the soil and lake adjacent to the farms. a total of eight samples were collected, and each has four sampling points; four sampling points, Eight parameters were analyzed for the water samples (pH, electrical conductivity (EC), Nitrate (No3-N), reactive phosphate (PO4), Biological oxygen demand (BOD), and chemical oxygen demand (COD), Sulfate (SO4), Total ammonia (T-NH3).in addition to this, the soil samples have been analyzed with five parameters ,( pH, CEC, EC, Phosphorus (P) and total Nitrogen (TN)) for the soil SS4 were chosen as a control sample which is relatively few meters far from the farm effluent. The results showed higher levels of TDS (292 to 1116), EC (507 to 1874), PH (7.97to 7.82), COD (291.2 to348.4) BOD (500 to 900) NO3-(1.09to 12.45) andPO43-(0.09 to 0.57) at the impaired sites where the effluent was directly discharged without treatment the concentrations also showed a very high increment when compared with the previous study results. And the same is true for the soils, EC(307to8780),PH,( 6.48to10.53)P(5.02to29),OC,( 0.41 to7.17) also has a great difference when compared with the control sites. . In addition to this, both the soil and water results were also compared with quality guidelines and standards, EPA, WHO, FAO to check if the concentrations of these parameters were within the permissible limits. The identified environmental impacts are water resource utilization, water and soil quality degradation, and land cover changesItem Assessing Volcanic Hazards from potential future Eruptions of Gebalaytu and Kurub Volcanos in the Tendaho Graben of Afar, North Eastern Ethiopia(Addis Ababa Universty, 2015-06) Teshome, Yonas; Asrat, Asfawossen (PhD)The paper assess the potential volcanic hazards pose by a Holocene Gebalaytu and Kurub volcanoes which are situated in the central afar depression at top of Tendaho Graben and adjacent to the active recent Manda-Harraro rift and west of Semera town about 5km and SE of the Manda -Harraro volcanic complex in the South Danakil region respectively. The petrographic and geochemical analysis of the volcanic rock is used to constraint the volcanic evolution and the origin of magma as a result the high Fe2O3 content of Gebalaytu rock tend to show tholeiitic affinity and sub alkaline group while Kurub volcano shows much more high Fe2O3 content however the Magma type is MORB at plate divergent and partial melting of the mantle since afar mantle plume is pushing the continental crust in afar. The associated rhyolitic rocks are formed by fractional crystallization of the basalt with little or no crustal contamination. The volcanoes have proximity to Semera city, Semera University, dry port a geothermal power sites, the Tendaho sugar estate and the Tendaho dam and water reservoir. The main road from Addis Ababa to Djibouti passes through the town and small villages around the volcanoes. The Tendaho graben as a whole is shows a potential of geothermal with different fumarolic activity Gebalaytu and Kurub volcanoes may pose potential hazards to population and important infrastructure. An assessment of the potential volcanic hazards from future eruption has been attempted based on the volcanoes past eruptive history. Tentative volcanic hazard maps and zones have been produced from four identified vents for Gebalaytu and one central vent for Kurub affecting an area over a moderate distance of 10km radius.Item Environmental Analysis of a Hydrologic System the Case of Tinishu Akaki River, Western Addis Ababa, Ethiopia(Addis Ababa Universty, 2007-06) Mohammed, Abdulshikur; Asrat, Asfawossen (PhD)Water Quality analysis of the Tinishu Akaki River System has been carried out with the objective of identifying where and when the river’s pollution and its consequences are more pronounced. And to determine what factors and / or processes prevail and control the situation spatially and temporally. To do so primary data on conventional water quality parameters; dissolved oxygen (DO), ammonia (NH3), Nitrate (NO3), Nitrite (NO2), PH, temperature(To) and total dissolved solids (TDS) was generated. In this study, five water samples were collected and analysed to represent the 2007 moderate flow period, the three spatial domains of the river (i.e. up, mid, and down streams) and the date when industrial effluents discharge is minimal. Besides, secondary data on the same and other physiochemical parameters for the years 1997, 1999, 2000, 2002/03, 2003/04, 2005/06, were collected from EPA monitoring unit and available literatures. After that, the available primary and secondary data were segregated between the three spatial domains, Low, Moderate, and High flow seasons, and Peak and little or No Industrial effluents discharge patterns. Then, by taking dissolved oxygen (DO) depletion as important water quality indicator pollution along the river course and its consequences have been analysed using spread sheet program. Moreover the physicochemical factors such as altitude, atmospheric pressure, temperature, Stream flow velocity, Salinity (TDS), BOD5, NH3, PO4, …etc. were used to justify the variation in DO level in the River water column. The results of the analyses depict that the extent of pollution is more severe when industrial effluents load is high and the river’s flow is low. Moreover, the midstream spatial domain is found to exhibit the worest situation in terms of pollution and or DO depletion. Above all, the increase in the concentrations of potentially harmful substances; heavy metals (Fe, Mn and Cr), ammonia, hydrogen sulphide, sulphates and phosphates is found to be associated with the generally declining DO level in the down stream direction. So as to abate this problem of water pollution, TMDLs (Total Maximum Daily Loads) and WLAs (Waste Load Allocations) for oxygen demanding wastes of industrial point sources is suggested to be the most cost effective and applicable mechanism of abatement that can assure the attainment of in stream water quality standards. Key Words: Dissolved Oxygen depletion, Tinishu Akaki River, Conventional Water Quality parameters, EthiopiaItem Environmental Analysis of the Areal Expansion and Lake Level Rise of Lake Beseka, Main Ethiopian Rift(Addis Ababa University, 2007-03-02) Abebe, Fassika; Asrat, Asfawossen (PhD)Lake Beseka has been drastically expanding from its original size of about 3Km2 (in the year 1964) to its current size of 41 km2 (in the year 2006) in the last four decades. Equally, the lake level has been rising at an average annual increment rate of 0.28m. The expansion of the lake has imposed several impacts on the social and natural environment of the surrounding area. The continuing rise of the lake level resulted in inundation of valuable grazing and farmland and watering points. Further rise could result in a complete inundation of the road and railway line passing nearby and substantial amount of the farm and grazing land in the vicinity. The ultimate increase in size of the lake may lead to the spillover of lake water into the river Awash, which due to the highly alkaline and saline nature of the former may affect the hydrochemistry of the river and the ecosystems down stream. This work addresses the areal expansion and lake level rise of Lake Beseka using an environmental analysis approach where water balance modeling and land use/land cover classifications and change detection analysis were employed. The water balance modeling revealed that surface water sources are not significant contributors to the lake level rise; rather sub-surface inflow, which includes spring discharges and deep groundwater sources are significantly affecting the lake level. Land use/land cover (LU/LC) change detection between the years 1973 and 1986 and between 1986 and 2003 were conducted, with the objective of creation of historical and current LU/LC maps and LU/LC change map of 1973, 1986 and 2003. The maps were derived utilizing standardized digital remote sensing classification techniques using three multi temporal Land sat scenes acquired on January 12, 1973 (MSS), January 28, 1986 (TM), and January 27, 2003 (ETM+). The change detection analysis revealed that the lake body has increased by 21.82 km2 (301.301%) between 1973 and 1986, and by 9.86 km2 (33.938%) between 1986 and 2003. Between 1973 and 2003, the lake has expanded by about 31.68 km2 (335%). The land use/land cover of the area significantly changed in the last three decades. This change has a direct effect on the expansion of the lake. Vegetation cover (shrub land) had been reduced by 65.41 km2 (30%). This in turn affects the runoff yielded from the catchment entering in to the lake. Unlike vegetation cover, degraded land had increased by 33.28 km2 (89.575%), which increases runoff entering in to the lake. Irrigation farmland which increased by about 13.63 km2 (5 7.411%). Water for irrigation is brought from Awash River that in turn is an input to the inflow of the lake; this has a great effect on areal expansion of the lake. The above result indicated that the land use/land cover change of the area has an additive effect on the lake’s areal expansion. LU/LC changes in the area are still intensified due to areal expansion of the Lake, population pressure, and unwise intervention of man with the environment (including unsatisfactory Irrigation Practices). Conservation of the natural resource, rehabilitation and management of the environment through land terracing and vegetating with productive plants are the envisage possible strategies that have to be taken to combat the existing and future adverse LU/LC changes that are associated with areal expansion of the Lake.Item Geo-Environmental Systems Analysis stream Climate Change Impact on Lake Abaya Water Level Approved by(Addis Ababa Universty, 2009-10) Belete, Azeb; Asrat, Asfawossen (PhD)The present study area is located in Abaya-Chamo basin, in the southern part of the Ethiopian Rift Valley. In this research project climate change impacts on levels of Lake Abaya is assessed by using appropriate techniques and the future lake level is forecasted based on scenario analysis conducted by changing the lake water balance parameters. Available time series data (satellite, hydrographic, climatic, land use- land cover, socio-economic, etc.) of the last two decades, in the area is used to determine the baseline, based on which modeling and lake level fluctuation is assessed .The water balance components of Abaya, the amount of runoff, precipitation, evaporation & storage changes, and their annual changes over the 1987-2005 period is systematically analyzed & formulated as a lake level forecast model. The model shows the average yearly inflow from river discharge, unguaged runoff and precipitation which are 750, 691 and 980 mcm, while the average outflow from evaporation is 2009mcm, respectively. The formulated model is applied in order to ascertain the effect of these components in the historic and future lake levels based on the sequences of 1987-2005 hydro-climatic conditions with different applications and assumptions. The assumptions are generally aims to test several different values of the observed hydro-climatic for future conditions. Based on the assumptions considered in the applications past hydro-climatic conditions observed and recorded as evidence and questionnaires taken from community living in study area, model applications 1A (tried to show the effect of river discharge and precipitation in the lake level rise), 2(tried to show the effect of lake evaporation in the lake level change), 4( the effect of precipitation amount on the surface of the lake and runoff from unguaged catchment in the lake level change) and 5(the effect of runoff amount increases by 50% of the present due to land use/land cover change by deforestation and agricultural land in the lake change) are chosen as a good predicator of Abaya lake level fluctuation. From the models it is observed lake level fluctuate mostly due to climatic factors and also man-made processes, precipitation and evaporation causes the major changes and also deforestation and agricultural expansion in the catchment had their own roleItem Geochemical Characterization of Sediment and Ground Water Contamination in Addis Ababa City from Petroleum Stations(Addis Ababa University, 2015-06-06) Hadush, Gebru; Asrat, Asfawossen (PhD)Addis Ababa is located on the shoulder of the Western Main Ethiopian Rift Escarpment in which the city is surrounded by mountain ridges from north and northwest and gentle slope to south and southeast part. The general surface and groundwater movement direction is dominated by north-south and east-west flow. Hydrogeologically the area characterized by fracture porosity and interstitial porosity and lithostratigraphic units from bottom to top includes Alaji basalts, Entoto silicics, Addis Ababa basalts, Nazareth group, and Bofa basalts associated. The main focus of the study is geochemical characterization of groundwater contamination in Addis Ababa mainly related to organic contaminants from petroleum station. Physico-chemical parameters: such as EC, TDS and PH, measured in-situ and from secondary sources; redox sensitive compounds and major ions analysis from secondary data; laboratory analysis of COD and Organic Carbon from ground water samples taken in the field were used to characterize the chemistry and possible contamination of groundwater. These secondary groundwater quality parameters were obtained from two different sources: from Addis Ababa Water and Sewerage Authority (AAWSA) and Addis Ababa water work design and supervision. Each parameter has been determined in order to assess the contaminant distribution in the study area. The values of the parameters have been evaluated with respect to the maximum acceptable standard level of WHO (World Health Organization) for drinking and groundwater. The result of physio-chemical analysis (TDS, EC H, redos-sensitive compounds) from groundwater wells reveals that the source of the organic contaminants in the study area is difficult to identify while physical evidence from gas stations and garages suggests that organic compounds are entering surface and subsurface environment. Finally for effective remediation program this work proposes in-situ capping for sediment and air sparging for groundwater.Item Geologcal and Geomorhological Characterization of The Dendi Caldera, West Central Ethiopia: Implications for Paleo-Environmental Reconstruction Using Lake Sediment Cores(Addis Ababa Universty, 2014-05) Zinaye, Bahru; Asrat, Asfawossen (PhD)The Dendi Caldera is located on the West Central Ethiopian Plateau, approximately 120 kilometers to West of Addis Ababa. It is located between 0804810011 - 0805210011 North latitude and 3705810011 - 3800410011 East longitude in Dendi kebele, Ginchi woreda, western showa zone, Oromiya regional state of Ethiopia. The caldera has almost elliptical shape with about 8.5 km diameter in its longest direction and 6.5 km in the shortest direction. There are two crater lakes making the shape of ‘8’ within this caldera, each with a circumference and an area of about 7.5 km and 4 sq. km respectively. The altitude varies between 2830m - 3270 m a.s.l.. The main objective of this research work is to study the geology, geochemistry and petrology of the Dendi caldera rocks, to construct the geological evolution of the caldera and to study the effect of the geology on the composition of the lake sediments in order to help reconstruct the paleoclimate using lake sediment core. The methods involved to achieve the objectives are desk studies about the area, fieldwork for mapping and sampling, petrographic studies, XRF analysis both on the lake sediment and rock samples, analysis and interpretation of data using different computer softwares. The caldera comprises different felsic volcanic products including trachyte, rhyolite and obsidian overlain by the pyroclastic deposits ignimbrite, volcanic surge and tuff. The rhyolite and trachyte are formed both as lava flow and lava dome. In some areas they show columnar joints. The surge deposit shows sedimentary structures like bedding and X-bedding. In thin section, the rhyolite, trachyte and ignimbrite has aphanitic and porpyritic aphanitic textures with alkali feldspar phenocrysts. The Trachyte also shows trachytic texture. On TAS diagram, the lavas are rhyolitic and trachytes/trachydacite and the pyroclastics are trachyandesite and basaltic andesite. In the spider diagrams (MORB normalized), Ba, Sr, P, Ti and Cr shows strong negative anomaly which verifies fractionation. The lava shows high Th and Nb with very low Sr. Rb/Nb and La/Nb ratios are very low while Rb/Sr ratio is very high in the Dendi volcanic products. These conditions show the only possible mechanism for the formation of the Dendi caldera is fractional crystallization of basaltic magma with limited or no crustal contamination. Five different sections have been identified based on the variation of different chemical and physical parameters applied on the lake sediment core. Section 4, with high grain size, MS, K, Si/Ti and Mn and low inc/coh, Sr/Ca, Zr/Rb and Rb/K, shows the driest period in the stratigraphy while section 2 shows the most humid period in the stratigraphy. The remaining sections spans between these two extremes. Key words: Dendi, Caldera, volcanic, felsic, fractional crystallization, paleoclimateItem Geological and Environmental Appraisal for the New Sanitary Landfill Site at Chebe Weregenu, North East of Addis Ababa, Ethiopia(Addis Ababa Universty, 2012-06) Mengistie, Netsanet; Asrat, Asfawossen (PhD)The Addis Ababa City Administration started a project to establish a new sanitary landfill site at Chebe Weregenu, which is 26 km from the city center of Addis Ababa. The project feasibility studies were already conducted. It is now under design study phase. In the feasibility studies, one of the main gaps noted was on the permeability of the residual soil, 1.164x10-4 to 2.329x10-4cm/sec which is below the standard. The standard requirement for sanitary landfill should be 1x10-7cm/sec or less. The permeability test result in the present research was found1.897 X10-7 to 1.085x10-8 cm/sec which is within the standard. The other gap was, both studies stated that the existing residual soil 0-5 meters is black cotton soil. In the present research, based on site investigation and test data the residual soil 0-4.5 meters have different soil profiles, black cotton soil and tuff material. The purpose of this research work is to identify possible gaps in the feasibility studies and to conduct geological and environmental appraisal of the Chebe Weregenu Sanitary Landfill Project. Eleven representative soil samples, two rocks and four water samples were collected from the site and were tested for the purpose of geological and environmental appraisal of the landfill site application. All representative soil sample test results complied with the standard requirements of permeability for clay cap and clay liner application. Regarding plasticity, the liquid limit value of seven out of ten samples complied with the standard requirement, but three are above the standard. The water quality test result was found fit for drinking purpose as per WHO standard. The water quality and soil fertility test results are base line data to be used as a reference point during the operational phase. This research filled the gap of the feasibility studies and further established different findings based on the primary data. Those results found within the standard range were presented as acceptable values and those test results out of the range were recommended for further investigation during the design studyItem Geology, Mineral Paragenesis, and Sequence Study of Bikilal Iron Mineralization in West Wollega; Western Ethiopia: Implication to Genesis.(Addis Ababa University, 2013-12-12) Rebso, Solomon; Tadesse, Solomon (Professor); Asrat, Asfawossen (PhD)Bikilal iron ore deposit is a Kiruna-type magnetite – ilmenite deposit in West Wollega Western Ethiopia. It is formed within syn-post tectonic intrusive gabbroic complex that intrudes the Precambrian gneiss. Bikilal gabbroic intrusion comprises olivine gabbro in the center, hornblende gabbro and hornblendite as dominant rock at the periphery of the intrusive as well as pegmatite, granite, migmatite, and anorthosite found as a minor lithology. Generally all lithological units are dipping SW with dip angles ranging from 350 ─ 750. The major structural trends in the study area are NW – SE following the regional lineament. Drill hole data shows that the rocks have layering. Hornblende gabbro and hornblendites with anorthosite are characterized by magnetite- ilmenite and apatite mineralization. Identification of different minerals and their textural relationships have been studied using ore and transmitted light microscope at the School of Earth Sciences, Addis Ababa University. The iron ore bearing hornblendite is classified into upper zone in the northern, middle zone in the north- eastern, and lower zone in the southern part of the study area. Bikilal iron deposit consists of magnetite, ilmenite, hematite, sulphides, apatite and gold. The principal ore minerals are magnetite and ilmenite. Apatite is the second most abundant mineral in association with magnetite and ilmenite. The sulfide minerals present are pyrite, chalcopyrite, pyrrhotite and pentlandite. Gold grains are found as isolated free grain in association with other sulphide minerals but commonly it is found as hatched inclusion inside chalcopyrite. The paragenetic sequence of mineralization was classified into four phases based on the microscopic study and existing geochemical data from previous works: Phase I = Silicates (olivine + pyroxene+ feldspar); Phase II =magnetite + massive- veinlet ilmenite + pyrite + pentlandite+ free gold; Phase III =exsolved ilmenite + hematite + pyrrhotite + gold; and Phase IV=chalcopyrite + geothite. In this work mineral association and paragenesis of Fe-Ti oxide-Py-Cu-Pyr-Ni-Au were identified and studied.Item Holocene Paleoclimate Reconstruction Inferred from Proxy Records in Speleothems from the Mechara Karst Area and Lake Archives From Tilo and Awassa Lakes, Ethiopia(Addis Ababa Universty, 2009-07) Zenebe, Aynalem; Asrat, Asfawossen (PhD)Holocene palaeoclimate records recovered from Bero_1 stalagmite of Holocene age, and, modern stalagmite samples Asfa_3, Ach_1 and Merc_1 and from lake Tilo and lake Awassa were compared in order to see the trends and nature of correlation and variability between the records. The major proxies used are the 18O of Bero_1 stalagmite together with the lamina width variation and the 18O of authigenic calcite from the lake records, and lake level variations reconstructed from the Ziway-Shalla lakes. The 18O proxy data was chosen because it varies with the variation in the precipitation amount and P/E ratios. The comparison made between 18O values of stalagmites showed they are poorly correlated. The comparison of 18O values between the Lake records and Bero_1 stalagmite again showed poor correlation. But the over all trend of isotopic variation between the lake and stalagmite records in the Holocene was similar in such a way that it is similar with the general early-middle-late Holocene moisture variation previously recovered from Paleo-lake level variations of the Ziway-Shalla lakes. The stalagmite 18O time series showed five major trends at a time scale of 100-120 years between 7800-7500, 7400-7300, 5400-5300, 4860-4800, and 4550-4470 yr BP and smaller variations at 10-20 years time scale within the major trends. Relatively enriched 18O values in Bero_1 stalagmite around 7650-7370 yr BP, 5300-5400, 4801-4860 and 4470-4530 yr BP and the recent late Holocene peak at the end of the growth phase correspond to the relatively lower precipitation periods in the Holocene. Similarly, the depleted 18O values between 7590-7450, 5890-5860, 5290-5320 corresponds to relatively wetter periods. Thicker stalagmite lamina deposited during relatively wet seasons and thinner lamina records during relatively dry periods further support the 18O trends with the precipitation amount variation. The 18O of authigenic carbonates from lake Tilo and Awassa also showed similar relatively depleted 18O values in the early Holocene wet period, and enriched values were recorded in dryer periods in response to the increased lake water evaporation effect. This study shows the comparison made between lake and stalagmite records follow similar trends through out the Holocene but with different magnitude of change; and the stalagmite records are further more important in providing a high resolution multi proxy records in order to understand the precipitation amount variability in the Holocene.Item Land Use/Land Cover Dynamics and Soil Degradation Assessement Using Remote Sensing and Gis: A Case Study of Jima Arjo Woreda (Western Ethiopia)(Addis Ababa Universty, 2009-06) Ebissa, Muleta; Asrat, Asfawossen (PhD)This study is aimed at assessing the spatio-temporal dynamics of land use/ land cover and soil degradation in Jima Arjo Woreda. Three different time landsat images (1973, 1986 and 2001) were classified into 7 major land use/cover classes through supervised classification: farm land, dense forest land, degraded forest land, open woodland, grassland, wet land and bare land. Post-classification change detection among the image data has been conducted. Accordingly, farmland and bare land has expanded with 15326.6ha and 769.897ha, respectively. Although the expansion is not continuous; open woodland increased by 6825.2ha and grassland by 6392.4ha over the period. However, vegetations particularly dense forest and the degraded forest land and wetlands were reduced greatly at varying rates of change per annum. Dense forest dropped down by 1686.5ha, degraded forest land reduced by 4264.7 and wetland by 8184.1ha. Land use/cover distribution across various slope categories and susceptibility to change has also assessed from the final state of the study period (2001) image data. With respect to land use/cove – slope distribution, steep slopes were made cultural landscapes (agricultural and settlement areas). Farm lands, particularly the intensively cultivated farms, were evident on steep slopes (above 250) and more than 60% of slopes above 120 were shared by the farmlands. Five levels of susceptibility to change: extremely susceptible, highly susceptible, moderately, low and none susceptible areas have been identified based on factors of accessibility, proximity to towns and rivers, agroclimate, soil, slope and the type of land cover in the area. Vegetations are signified as the most susceptible classes. This has been realized in that 94.1% of the high to extremely high susceptibility level has been shared by dense forests. Soil Loss has been estimated using USLE model on the basis of the adapted methodology and parameters for Ethiopian highland conditions. The estimated soil loss for the study area ranges from 0.35 – 184.4t/ha/yr with mean annual loss of 20.6t/ha. Highly sever soil loss (>60t/ha/yr) has been recognized over 5.9% in the area. This is more evident on the farm lands. The low soil loss (<1t/ha/yr) experienced over 10% of the area where vegetations (particularly the grassland and dense forest land) were recognized. Key Words: land use/land cover dynamics, land use/cover susceptibility to change, soil degradation, USLE, Annual Soil Loss EstimationItem Modeling Site Suitability for Wind Farm Using Remote Sensing and Gis: The Case of Adama Woreda(Addis Ababa Universty, 2009-06) Belay, Eyaya; Asrat, Asfawossen (PhD)Adama Woreda has good wind resource potential for grid based wind farm establishment. But, selecting sites for wind farm in the study area is a complex process involving not only technical but also physical, economical, social and environmental considerations. This study focuses on mapping wind farm suitability in Adama Woreda. The major data used were topographic map (1:50,000), Landsat image (2005), and GIS data layers such as roads, towns, transmission line, geology, land use and slope. The factors were developed in the GIS and Remote Sensing environment then weighted and overlaid by the principle of pairwise comparison. Once the wind farm suitability map has been completed, sites were evaluated with respect to the factors. The finding of this study shows that there is sufficient area for wind farm establishment in Adama Woreda with the most suitable sites located in the southeastern, northeastern and southern parts. 85% of the most suitable sites are laid on agricultural land which is relatively compatible with wind farm. 38.5 and 21.24 % of most suitable area are laid on recent aphyric basalts and ash flow tuffs respectively which are most suitable and moderately suitable areas from engineering point of view.Item Modelling and Forecasting Awassa Lake Level Fluctuation(Addis Ababa Universty, 2007-03) G/Michael, Habtom; Asrat, Asfawossen (PhD)Lake Awassa is located in the central main Ethiopian rift valley. The Lake is important water resource in the study area and is used for irrigation, municipal and domestic water supplies as well as recreational purposes. Beside its importance, the level of the lake has changed dramatically over the past two decades. Because of this, the lake has attracted considerable attention in recent years especially when the lake flooded the surrounding area including Awassa town which is established adjacent to the lake. Fundamental for understanding the lake level fluctuation requires knowledge of the lake's water balance and its response to human induced and climatic changes in the hydrologic regime. The present study develops a water balance forecast model for Lake Awassa. The model uses annual values of surface runoff (gauged and ungauged), evaporation, precipitation and groundwater outflow to simulate past lake levels. For this reason, the model was calibrated using multiple linear regressions and ARIMA model fit using SPSS software. The calibrated model was verified and used to forecast future lake level based on various selected applications and assumptions. The model result shows that the surface runoff and evaporation accounts about 81% and 38% in short term lake level fluctuation but in long term lake level fluctuation precipitation and evaporation accounts 45% and 73%respectively. This is mainly the result of land use/cover changes which causes the runoff to increase and evaporation to decrease. If this continues the lake would be a treat to the surrounding area and the town might be at risk if remedial measures are not considered. Although the environmental implications of a given lake level are beyond the scope of this study, the model provides an essential tool for water policy and management decisions in the Awassa catchment.